Three-dimensional objects generated by an additive manufacturing process are formed in a layer-by-layer manner. In one example of additive manufacturing, the object is generated by coalescing and solidifying portions of layers of build material. In examples, the build material may be in the form of a powder, fluid or sheet material. The intended coalescence, solidification and/or physical properties may be achieved by printing an agent onto a layer of build material. Energy may be applied to the layer and the build material which is coated with the agent coalesces and solidifies upon cooling. In other examples, 3-D objects may be generated by using extruded plastics or sprayed materials as build materials which solidify to form an object.
Some printing processes for generating three-dimensional objects use control data generated from a model of a 3-D object. This control data may, for example, specify locations at which to apply an agent to a build material, or where a build material may itself be placed.